m68k: Fix off-by-one calendar month

This fixes a bug in read_persistent_clock() which causes the system
clock to lag the Real Time Clock by one month. The problem was noticed
on a Mac, but theoretically it must also affect Atari, BVME6000 and Q40.

The tm_mon value in the struct rtc_time passed to mach_hwclk() is
zero-based, and atari_mste_hwclk(), atari_tt_hwclk(), bvme6000_hwclk(),
mac_hwclk() and q40_hwclk() all make this adjustment. Unfortunately,
dn_dummy_hwclk(), mvme147_hwclk(), mvme16x_hwclk(), sun3_hwclk() and
sun3x_hwclk() fail to decrement tm_mon.  Also m68328_hwclk() assumes
a one-based tm_mon.

Bring these platforms into line and fix read_persistent_clock() so it
works correctly on all m68k platforms.

The datasheets for the RTC devices found on the affected platforms
all confirm that the year is stored as a value in the range 0-99 and
the month is stored as a value in the range 1-12. Please refer to the
datasheets for MC146818 (Apollo), DS1643 (MVME), ICM7170 (Sun 3)
and M48T02 (Sun 3x).

Reported-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/m68k/mvme147/config.c b/arch/m68k/mvme147/config.c
index 8778612d1f31..f8a710fd84cd 100644
--- a/arch/m68k/mvme147/config.c
+++ b/arch/m68k/mvme147/config.c
@@ -153,12 +153,14 @@ int mvme147_hwclk(int op, struct rtc_time *t)
 	if (!op) {
 		m147_rtc->ctrl = RTC_READ;
 		t->tm_year = bcd2int (m147_rtc->bcd_year);
-		t->tm_mon  = bcd2int (m147_rtc->bcd_mth);
+		t->tm_mon  = bcd2int(m147_rtc->bcd_mth) - 1;
 		t->tm_mday = bcd2int (m147_rtc->bcd_dom);
 		t->tm_hour = bcd2int (m147_rtc->bcd_hr);
 		t->tm_min  = bcd2int (m147_rtc->bcd_min);
 		t->tm_sec  = bcd2int (m147_rtc->bcd_sec);
 		m147_rtc->ctrl = 0;
+		if (t->tm_year < 70)
+			t->tm_year += 100;
 	}
 	return 0;
 }